The invention relates to oil production from the seafloor to a tensioned leg platform and in particular to a connector assembly for tying back the production casing from the seafloor to the TLP wellhead.
Offshore oil wells may be drilled from a floating platform and therafter produced to a later-installed tensioned leg platform. Such a procedure requires the running of casing strings from the platform deck to the seafloor wellhead. Tubing is then run, surface production trees installed, and the well is produced in a conventional manner.
When running a conductor and attaching it to the wellhead, axial alignment between the wellhead and the conductor is a problem. A solution for this is described in co-pending application Ser. No. 120,200, filed Feb. 11, 1980, now Patent No. 4,343,495. A downwardly-extending funnel with two bearing surfaces surrounds the wellhead and achieves the angular alignment. Final alignment is achieved when the connector is brought into abutting relationship with the upper edge of the wellhead where the seal is effected. For production to be to a fixed platform, there would be no additional motion once the connection has been made. A tensioned leg platform, however, introduces movement of the upper end of the riser. Accordingly, a large diameter conductor experiences excessive strains and stresses for a given deflection. A smaller diameter production riser is preferable since this results in lower stresses for a given offset movement.
Even with the smaller conductor, however, there are repeated and varying bending moments placed on the wellhead connection during normal operation. This will cause unloading, or even movement, of the seal and a loss of pressure integrity thereof. Accordingly, an apparatus is to be preferred which will avoid failure of the seal caused by the deflection of the production riser.